11 research outputs found
Field evidence for colony size and aseasonality of breeding and in Ansell’s mole-rat, Fukomys anselli (Rodentia: Bathyergidae)
Ansell’s mole-rat, Fukomys anselli, is a cooperatively breeding bathyergid endemic to the
Lusaka Province of Zambia. During a 12-month field study involving the capture of 33 colonies
of mole-rats, the number of occupants, breeding females and sex ratio within colonies were
recorded. While thirty of these social groups contained a single breeding queen, three were
found to exhibit plural breeding among females, having two queens present simultaneously.
Mean±S.E.M. colony size was 8.7±2.2 (range 6–16,n=33). The occurrence of plural breeding
and small group size is consistent with the predictions of the aridity food distribution hypothesis
for social species inhabiting mesic habitats. The sex ratio of the population was skewed
towards females at 1.2:1. The mean mass of adult males was 63.0 ± 18.3 g (range 36.7–110.3,
n=87) while that for adult females was 52.9±11.8 g (range 35.1–77.8, n=86). Pregnant and
lactating females were found throughout the study period from February 2009 to February
2010, indicating an aseasonal pattern of breeding in this species. Autopsy of individuals
(n = 288) from the 33 colonies revealed a total of 19 pregnant females. Nine of these were in
the latter stages of pregnancy and mean litter size was determined as 2.7 pups (range 1–4).
Collectively, these new data reveal that Fukomys anselli share many similarities in life history
and reproductive traits with the phylogentically closely related giant Zambian mole-rat,
Fukomys mechowii.A Department of Science and Technology and National
Research Foundation SARChI Chair in Mammal
Behavioural Ecology and Physiology to NCB.
AMS was the recipient of a postdoctoral fellowship
from the SARChI chair.http://www.bioone.org/loi/afzoab201
Digging for answers : contributions of density- and frequency-dependent factors on ectoparasite burden in a social mammal
Due to the density-dependent nature of parasite transmission parasites are generally assumed to constrain the evolution of sociality. However, evidence for a correlation between group size and parasite burden is equivocal, particularly for mammals. Host contact rates may be modified by mobility of the host and parasite as well as social barriers. In the current study, we used the common mole-rat (Cryptomys hottentotus hottentotus), a social subterranean rodent, as a model system to investigate the effect of host density and frequency of contact rates on ectoparasite burdens. To address these factors we used a study species that naturally varies in population densities and intergroup contact rates across its geographic range. We found that ectoparasite prevalence, abundance and species richness decreased with increasing host density at a regional scale. At the same time, measures of parasite burden increased with intergroup contact rates. Ectoparasite burdens decreased with colony size at the group level possibly as a result of increased grooming rates. Equating group size with population density might be too simplistic an approach when assessing parasite distributions in social mammals. Our data suggest that frequency-dependent mechanisms may play a much greater role at a population level than density-dependent mechanisms in determining parasite distributions in social species. We suggest that future studies should explicitly consider behavioural mechanisms that may affect parasite distribution.NRF-SAR Chair for Mammalian Behavioural Ecology and Physiology to NCB.University of Pretoria Research Fellowship.http://link.springer.com/journal/4422017-02-26hb201
Reproduction in the East African root rat (Tachyoryctes splendens ; Rodentia : Spalacidae) from Tanzania : the importance of rainfall
The East African root rat, Tachyoryctes splendens (RĂĽppell, 1835) is a solitary subterranean
rodent mole. The present study investigated breeding patterns in both sexes of T. splendens from
data collected at monthly intervals over an entire calendar year. The study focused on the
analyses from post mortem examination of males and females to assess the presence of foetuses,
gonadal histology, reproductive tract morphometrics, measurement of gonadal steroids (plasma
progesterone and oestradiol-17β in females and testosterone in males) and field observations
(i.e., the presence of infants, juveniles, sub-adults and lactating females). The objective of this
study was to assess if the reproductive biology of the root rat reflected the bimodal pattern of rainfall that is characteristic of East Africa. Rainfall has been suggested to trigger breeding in
many subterranean rodents and as a consequence, this study aimed to assess the relationship
between rainfall and reproductive characteristics of T. splendens. Peaks in mean gonadal mass,
increases in concentration of reproductive hormones and the presence of Graafian follicles and
corpora lutea in the ovaries of females, and testes mass, seminiferous tubule diameter and
testosterone titre mirrored the annual peaks of precipitation at the study area. Together with field
observations of the temporal occurrence of pregnancies, infants, juveniles and sub-adults, the
data show that T. spendens cues its breeding with the patterns of rainfall, such that offspring are
born in the latter half of each rainy season, from April to July and November to December.University of Dar es Salaam [UDSM–World Bank Fund (C1B1) ], Tanzania.South African Department of Science and Technology (DST)/National Research Foundation (NRF) SARChI Chair for Mammal Behavioural Ecology and Physiology, University of Pretoria.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1469-7998hb201
Molecular evolution of the hyaluronan synthase 2 gene in mammals : implications for adaptations to the subterranean niche and cancer resistance
The naked mole-rat (NMR) Heterocephalus glaber is a unique and fascinating mammal
exhibiting many unusual adaptations to a subterranean lifestyle. The recent discovery of
their resistance to cancer and exceptional longevity has opened up new and important
avenues of research. Part of this resistance to cancer has been attributed to the fact that
NMRs produce a modified form of hyaluronan—a key constituent of the extracellular
matrix—that is thought to confer increased elasticity of the skin as an adaptation for
living in narrow tunnels. This so-called high molecular mass hyaluronan (HMM-HA)
stems from two apparently unique substitutions in the hyaluronan synthase 2 enzyme
(HAS2). To test whether other subterranean mammals with similar selection pressures
also show molecular adaptation in their HAS2 gene, we sequenced the HAS2 gene for 11
subterranean mammals and closely related species, and combined these with data from 57 other mammals. Comparative screening revealed that one of the two putatively important
HAS2 substitutions in the NMR predicted to have a significant effect on hyaluronan
synthase function was uniquely shared by all African mole-rats. Interestingly, we also
identified multiple other amino acid substitutions in key domains of the HAS2 molecule,
although the biological consequences of these for hyaluronan synthesis remain to be
determined. Despite these results, we found evidence of strong purifying selection acting
on the HAS2 gene across all mammals, and the NMR remains unique in its particular
HAS2 sequence. Our results indicate that more work is needed to determine whether the
apparent cancer resistance seen in NMR is shared by other members of the African molerat
clade.DST-NRF SARChI Chair for Behavioural Ecology and Physiology.European Research
Council.http://rsbl.royalsocietypublishing2016-05-31hb201
Family wide molecular adaptations to underground life in African mole-rats revealed by phylogenomic analysis
During their evolutionary radiation, mammals have colonized diverse habitats. Arguably the subterranean niche is the
most inhospitable of these, characterized by reduced oxygen, elevated carbon dioxide, absence of light, scarcity of food,
and a substrate that is energetically costly to burrow through. Of all lineages to have transitioned to a subterranean niche,
African mole-rats are one of the most successful. Much of their ecological success can be attributed to a diet of plant
storage organs, which has allowed them to colonize climatically varied habitats across sub-Saharan Africa, and has
probably contributed to the evolution of their diverse social systems. Yet despite their many remarkable phenotypic
specializations, little is known about molecular adaptations underlying these traits. To address this, we sequenced the
transcriptomes of seven mole-rat taxa, including three solitary species, and combined new sequences with existing
genomic data sets. Alignments of more than 13,000 protein-coding genes encompassed, for the first time, all six
genera and the full spectrum of ecological and social variation in the clade. We detected positive selection within the
mole-rat clade and along ancestral branches in approximately 700 genes including loci associated with tumorigenesis,
aging, morphological development, and sociality. By combining these results with gene ontology annotation and
protein–protein networks, we identified several clusters of functionally related genes. This family wide analysis of molecular
evolution in mole-rats has identified a suite of positively selected genes, deepening our understanding of the
extreme phenotypic traits exhibited by this group.The European Research Council (ERC Starting grant 310482 [EVOGENO]) awarded to S.J.R.; the DST-NRF SARChI Chair of Mammalian Behavioral
Ecology and Physiology (grant number 64756) (funds to N.C.B.).http://mbe.oxfordjournals.orghb201
Phylogeography and cryptic diversity of the solitary-dwelling silvery mole-rat, genus Heliophobius (family: Bathyergidae)
Alongside the eusocial naked mole-rat, Heterocephalus glaber, Heliophobius
argenteocinereus represents the second oldest lineage within the African mole-rat family
Bathyergidae, and phylogenetically intermediate between the East African Het. glaber and the
South African genera Bathyergus and Georychus. Across its geographic range, Hel..
argenteocinereus is widely distributed on both sides of the East African Rift System (EARS),
and is a key taxon for understanding the phylogeographic patterns of divergence of the family
as a whole. Phylogenetic analysis of 62 mitochondrial cyt b sequences, representing 48 distinct
haplotypes from 26 geographic locations across the range of Heliophobius, consistently and
robustly resolved six genetically divergent clades that we recognize as distinct evolutionary
species. Early species descriptions of Heliophobius were synonymized into a monotypic taxonomy
that recognized only Hel. argentocinereus. These synonyms constitute available names for these
rediscovered cryptic lineages, for which combined morphological and genetic evidence for
topotypical populations endorses the recognition of six to eight distinct taxa. Bayesian estimates
of diver- gence times using the fossil Proheliophobius as a calibration for the molecular
clock suggest that the adaptive radiation of the genus began in the early Miocene, and that
cladogenesis, represented in the extant species, reflects a strident signa-
ture of tectonic activity that forged the principal graben in the EARS.SYNTHESYS grant (BE-TAF-289), grants from the National Research Foundation, the University of Pretoria South Africa (to NCB) and the ERANDA
and Bay Foundations (FC).http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1469-7998ab201
Sweeping the house clean : burrow architecture and seasonal digging activity in the East African root rat from Tanzania
We investigated changes in burrow architecture and fractal dimension across
seasons and between the sexes in the solitary East African root rat Tachyoryctes
splendens over an entire calendar year. The basic burrow system comprised a main
tunnel reticulating into foraging tunnels, a nest consisting of food store chamber,
latrine and sleeping area, and a bolt hole. Main tunnel length was strongly affected
by sex, and contrary to expectations, it was longer for females than for males
(during both the dry and the wet seasons). The number and the length of foraging
tunnels were affected by both sex and season, with females’ burrows having more
foraging tunnels than males in both the dry and the wet seasons. Females also had
burrows with higher fractal dimension than males, while fractal dimension
increased with burrow length for both sexes. We suggest that unlike the solitary
bathyergid mole-rats, male T. splendens do not construct larger burrows than
females in the search for mates, but rather females have larger burrows with more
foraging tunnels resulting from the increased need for provisioning of their young.University of Dar es Salaam (UDSM) World Bank Fund (C1B1 of the University of Dar as Salaam, Tanzania. NCB acknowledges funding from the South African DST/NRF SARChI Chair for Mammal Behavioural Ecology and Physiology,University of Pretoria.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1469-79982015-08-31hb201
Molecular evolution of growth hormone and insulin-like growth factor 1 receptors in long-lived, small-bodied mammals
Mammals typically display a robust positive relationship between lifespan and body size. Two groups that deviate
markedly from this pattern are bats and African mole-rats, with members of both groups being extremely
long-lived given their body size, with the maximum documented lifespan for many species exceeding
20 years. A recent genomics study of the exceptionally long-lived Brandt's bat, Myotis brandtii (41 years), suggested
that its longevity and small body size may be at least partly attributed to key amino acid substitutions
in the transmembrane domains of the receptors of growth hormone (GH) and insulin-like growth factor 1
(IGF1). However, whereas elevated longevity is likely to be common across all 19 bat families, the reported
amino acid substitutionswere only observed in two closely related bat families. To test the hypothesis that an altered
GH/IGF1 axis relates to the longevity of African mole-rats and bats,we compared and analysed the homologous
coding gene sequences in genomic and transcriptomic data from 26 bat species, five mole-rats and 38
outgroup species. Phylogenetic analyses of both genes recovered themajority of nodes in the currently accepted
species tree with high support. Compared to other clades, such as primates and carnivores, the bats and rodents
had longer branch lengths. The single 24 amino acid transmembrane domain of IGF1Rwas found to bemore conserved
across mammals compared to that of GHR.Within bats, considerable variation in the transmembrane domain
of GHR was found, including a previously unreported deletion in Emballonuridae. The transmembrane
domains of rodents were found to be more conserved, with mole-rats lacking uniquely conserved amino acid
substitutions. Molecular evolutionary analyses showed that both genes were under purifying selection in bats
andmole-rats. Our findings suggest thatwhile the previously documentedmutations may confer some additional
lifespan to Myotis bats, other, as yet unknown, genetic differences are likely to account for the long lifespans
observed in many bat and mole-rat species.DST–NRF SARChI Chair for Behavioural Ecology and Physiology (64756), the European Research Council (310482 EVOGENO) and the National Science Foundation (DEB-0949759).http//www.elsevier.com/locate/genehb201
Field evidence for aseasonality of reproduction and colony size in the Afrotropical giant mole-rat Fukomys mechowii (Rodentia: Bathyergidae)
The giant mole-rat, Fukomys mechowii is a cooperatively breeding subterranean mole-rat exhibiting a reproductive division of labour in which usually one, or occasionally two, females are responsible for procreation. In a field study that involved complete excavation of 32 burrow systems, mean colony size was 9.9 individuals (range 7-16). Pregnant reproductive females were found throughout the study period (September 2005 until June 2006), supporting preliminary evidence that reproduction occurs throughout the year. Of the 32 colonies sampled, 10 of 14 in which the reproductive female could be identified as pregnant contained a single reproductive female, while four had two females breeding simultaneously (plural breeding). The population sex ratio was skewed towards females at 1:1.46. Autopsy of pregnant reproductive females (n = 18) revealed that the production of two (10 / 18 pregnancies) or three (7 / 18) offspring was the norm, with one case of four embryos being present. These new data increase our fragmentary knowledge of the natural history of this little-studied species
Ontogenetic variation and craniometric sexual dimorphism in the social giant mole-rat, Fukomys mechowii (Rodentia: Bathyergidae), from Zambia
The degree of maxillary molar tooth-row eruption and wear were used to assign samples of the
social giant mole-rat, Fukomys mechowii, from Zambia, into nine relative age classes in order
to assess ontogenetic (age) variation and craniometric sexual dimorphism, with reference to
body mass. Univariate and multivariate statistical analyses showed craniometric differences
between age classes 1–3 and age classes 5–9, with age class 4 being intermediate between
these two age class groupings. This suggests that age class 4 lies at a point on a hypothetical
growth curve where growth begins to stabilize. The intermediate placement of age class 4
in multivariate space broadly coincided with body mass categorizations into juveniles
(age classes 1–3; <100 g), subadults (age class 4; c. 100–150 g), and adults (age classes 5–9;
>150 g). The analyses also revealed the absence of sexual dimorphism in the relatively younger
age classes 1–4 but its presence in the relatively older age classes 5–9, and these results are
supported by data on body mass. These results may have implications in our understanding of
the population and social structures, and reproductive strategies in this little-studied giant
mole-rat